Process of separating wax from oils



E. M-L DONS ET AL PROCESS QF SEPARATING WAX FROM OILS July 4, 1939.

Filed Jan. 9, 1957 /Nl/ENTo/es: E. M. Jo/v6, a.. MAPf-, y oww m26@FITToRA/En Patented July 4, 1939 UNHTED STATES raar OFFICE Eddie M. Donsand Dwight B. Mapes, rllulsa, Okla.

assignors to Mid-Continent Petroleum Corporation, Tulsa, Okla., acorperation of Delaware Application January 9,

2 Claims.

This invention relates to processes of separating wax from oils. Priorto this invention, propane and other normally gaseous solvents have beenemployed as selective dewaxing solvents, the operations being carriedout under pressure which is gradually reduced to permit evaporation ofsome of the solvent, and thereby chill the remaining solution to thedewaxing temperature. An advantage gaine-d by the old use of suchnormally gaseous dewaxing solvents lies in the refrigeration which isreadily obtained by evaporating a predetermined portion of the solvent.However, disadvantages appear in the requirement for relatively highpressures throughout the system, including the iilters, or the like,where the precipitated wax is separated from the chilled solution. Inusing propane a further disadvantage lies in the extremely low dewaxingtemperature, which is usually about 40 F., requiring very expensiveequipment to withstand the extraordinary temperature changes, especiallywhen subjected to the operating pressures. The cost of chilling thesolution toa temperature far below F. is another expensive factor in theuse of propane and the like.

Normally liquid dewaxing solvents provide the advantage of operatingunder approximately atmospheric pressure, in more simple and lessexpensive equipment, as Well as the advantage of dewaxing at much highertemperatures, for example about 0 F. However, the old methods of usingthese normally liquid dewaxing solvents lack the advantage ofevaporation in the solution to provide the dewaxing temperature.

An object of the present-invention is to obtain advantages of both ofthe old dewaxing processes, without incurring the outstandingdisadvantages of either type. More specically stated, an object is to souse a normally gaseous refrigerant that it is not necessary to employall of the high pressure conditions, nor the very expensive equipmentrequired for extremely low temperatures; at the same time avoiding theexcessive operating expense involved in producing such extremetemperatures. Otherwise stated, an object is to employ a normally liquiddewaxing solvent, so as to obtain the advantage of dewaxing atcomparatively high temperatures in a relatively simple and inexpensivesystem, while obtaining the advantage of evaporation in the solution toprovide the desired low temperature.

In one form of the invention, we producev a solution of wax-containingoil and normally liquid dewaxing solvent in the proportions required forprecipitation of the wax to be removed.

193'?, Serial No. 119,751

To this dewaxing solution we add a refrigerant which is mixed with thesolution to perform its function as a cooling agent, and then removedbefore the wax is separated from the solution. The normally gaseousrefrigerant may be propane, methyl chloride, dimethyl ether, or anyother normally gaseous material adapted to be introduced in a liquidstate and removed by evaporation which results in the chilling.

The normally liquid dewaxing solvent may be employed in quantitiessufficient for all of the selective action desired in the precipitationof the wax, and in this event, the dewaxing may be carried out atrelatively high temperatures. The normally gaseous material may beemployed for refrigeration alone, so as to avoid objections to thepresence of such material during the operation of removing the wax. Forexample, in using propane as a refrigerant, we endeavored to remove allof the propane from the chilled solution, as the presence of propaneduring the operation of removing the wax wouldrrequire a lowertemperature for the precipitation of the wax. However, in commercialpractice, it is not necessary to remove all of the propane, or otherrefrigerant, as a small quantity of this material will not substantiallyinterfere with the operation, Therefore, it is to be understood thatwhen we refer to evaporation of the refrigerant, we mean a substantialevaporation required for the cooling, and this does not require acomplete removal of the refrigerant from the solution.

Another object is to produce a continuous dewaxing system wherein therefrigerant is introduced into and removed from the dewaxing solution,without requiring the use of very expensive and troublesome batchChillers, which are ordinarily employed in commercial systems usingnormally gaseous dewaxing solvents. In one form of the invention, anormally lgaseous refrigerant is evaporated in the dewaxing solutionwhile a stream of the mixture is flowing through an elongatedpassageway, thereby gradually chilling a continuous stream of thesolution as it progresses toward the dewaxing station. Or, if desired,the continuous stream of dewaxing solution may be chilled by introducinga cold stream of refrigerant into the flowing solution while it isadvancing toward the dewaxing station. The cooperative effect of thesetwo different features can be conveniently obtained by introducing astream of chilled refrigerant into the continuous stream of dewaxingsolution, thereby cooling the stream of solution, and thereafterevaporating the refrigerant in the owing stream to continue the chillingoperation.

Another object is to produce a dewaxing process wherein the solution tobe dewaxed can be very quickly chilled, with the result of precipitatingwax in a form that can be very readily removed by filtration.

With the foregoing and other objects in view, the invention comprisesthe novel process hereinafter more specifically described an-d shown inthe accompanying drawing, which illustrates one form of the invention.However, it is to be understood that the invention comprehends changes,variations and modifications within the scope of the claims hereuntoappended.

The drawing is a diagrammatical view of a dewaxing system embodyingfeatures of this invention.

In the system illustrated by this drawing, the oil stock to be dewaxediiows from a tank I through a pipe 2 leading to a heater or cooler 3where the oil stock may be heated or cooled to the desired temperature.The stream of oil then flows through a pipe 4 to a mixer 5. A normallyliquid dewaxing solvent fiows from a supply tank 6 through a heater orcooler 'I and thence to the pipe 4 where it enters into the stream ofoil. The constituents of the two streams, at a temperature desired toform the solution, are mixed in the mixer 5 and conducted through a heatexchanger 8 to a pipe 9 leading to a pump I0 which forces the solutionthrough a pipe II to a mixer I2, where the solution is mixed with arefrigerant.

A liquefied normally gaseous refrigerant flows from a supply tank I3through a pipe I4 to a heat exchanger I5 where it is cooled, and thenconducted through a pipe I6 to a chamber I'I. The liquefied refrigerantis under a pressure which may be reduced in the chamber I'I to evaporatea L portion of the liquid, thereby cooling the remaining liquid. Astream of this cooled refrigerant is discharged from the chamber I1through a pipe I8 to a pump I9 which forces the cold liquid into the pmixer I2, where the cold stream unites with the :f stream of solutionfrom the pipe- I I.

The solution to be dewaxed is very suddenly cooled by the cold stream ofrefrigerant in the mixer I2.

The two streams are constantly transmitted into the mixer I2, and theresultant cooled stream of solution and refrigerant, together withprecipitated wax, is preferably conducted through a pipe 28 to anelongated chilling passageway formed by a coil of pipe 2I. It is to beunderstood that the v mixture enters this elongated passageway under apressure high enough to retain the normally gaseous refrigerant in aliquid condition, but as the mixture progresses through said passagewaythe pressure is gradually reduced, so as to gradually evaporate therefrigerant, and thereby gradually cool the material to be dewaxed. Thisgradual reduction in pressure may be due to high pressure at the inletof the elongated pipe 2I compared to low pressure at the discharge endof the pipe, and if desired, various mechanical expedients may beemployed to aid in reducing the pressure. The desired result can beobtained by using pipes o-f uniform diameter in the chilling coil 2l, ora flaring condition can be obtained by gradually increasing the diameterfrom a relatively small dimension at the inlet of the coil 2| to alarger diameter at the outlet. The discharge end of the coil 2l hereinshown is connected by means of a pipe to a chamber 23 which may be underabout atmospheric pressure, or under a partial vacuum.

Approximately all of the refrigerant may be evaporated in the stream ofsolution flowing through the elongated chilling passageway at 2I, andthe resultant gas may be separated from the chilled solution in anysuitable manner. For example, this gas may be released in the chamber 23under about atmospheric pressure, or lower, and conducted through a pipe24 to a compressor 25 which discharges through a pipe 25 to a cooler 2I.The gaseous refrigerant is thus condensed and returned in a liquid statethrough pipe 28 leading from the cooler 21 to the supply tank I3.

It will be observed that the refrigerant may be forced into and thenremoved from a constant stream of the solution to be dewaxed. In otherwords, the normally gaseous refrigerant may be utilized solely forrefrigerating, while normally liquid dewaxing solvent performs theselective action desired for dewaxing. In this event, all of the wax canbe precipitated at relatively high temperatures, for example, 0 F. orhigher.

After being chilled by the refrigerant and then separated therefrom, themixture to be dewaxed may be transmitted from the chamber 23, through apipe 29 to a continuous rotary lter 30, where the wax is constantlyremoved through a conductor 3 I, while the dewaxed solution isconstantly discharged through a pipe 32 leading to a tank 33. This coolsolution may be transmitted through a pipe 34 to the heat exchanger I5,thence through a pipe 35 to the heat exchanger 8, and pipe 36 leading toa solvent recovery system 31. At this point, the normally liquid solventmay be distilled from the dewaxed oil and returned through a pipe 38 tothe supply tank 6.

In carrying out the process, a substantial advan` tage will usually beobtained by evaporating the refrigerant in the mixed stream flowingthrough the elongated passageway formed by the chiller 2|. However, ifdesired, the mixture of refrigerant and dewaxing solution may betransmitted from the pipe 20 through a by-pass 39 leading directly intothe low pressure chamber 23, where the refrigerant may be graduallyevaporated in the usual manner to chill the wax-containing solution.

It is to be understood that the refrigerant may be united with thesolution at any desired point and at any desired temperature. However,an advantage is gained by the extremely rapid chilling obtainable fromthis process. The chilled stream of refrigerant at an extremely lowternperature, for example, -40 F. or considerably lower, may be forcedinto the stream of dewaxing solution, so as to quickly chill thesolution at a rate in excess of 20 F. per minute (1200D F. per hour),which results in sudden precipitation of wax. We have found that thisresult can be very economically obtained without causing any diflicultyin filtering the precipitated wax from the solution. The extremely lowtemperature of the refrigerant can be conveniently obtained by evaporating a portion of the normally gaseous liquid in the chamber I'I, thegas being discharged through a pipe 4U to a compressor 4I which forcesthe compressed refrigerant into the return line 26, while the stream ofchilled liquid is constantly discharged through the pipe I 8 to themixer I2.

The invention is not limited to the use of any particular refrigerant,examples of which are found in propane, methyl chloride, dimethyl ether,and other normally gaseous liquids. I-Iowever, it is usually convenientto use mixtures of normally gaseous hydrocarbons, such as commercialpropane. Any suitable normally liquid dewaxing solvent may be employed.Specific examples of such dewaxing solvents include butyl acetate, amylacetate, isopropyl acetate, and blends of these solvents, or a blend ofone of said solvents and dichlorethyl ether. Other examples appear inmixtures of acetone and benzol, and normally liquid solvents of thistype. However, the invention is not limited to the use of any of thedewaxing solvents herein specified.

One volume of the oil to be dewaxed may be dissolved in about two tothree volumes of the normally liquid dewaxing solvent, using a quantityof this solvent suiiicient for precipitation of all of the wax to beremoved in the process. Numerous liquid solvents of this kind can beemployed to obtain a pour point within 20 F. of the dewaxingtemperature, and in using a number of these normally liquid solvents,the ultimate pour point will be equal to or very substantially below thedewaxing temperature, which is quite different from the extremely 10Wtemperatures required in using propane as a selective dewaxing solvent.The oil and normally liquid dewaxing solvent may be heated at 3 andrespectively, to a temperature that will result in complete solution ofthe oil and wax in the solvent, and then cooled to precipitate the wax.A

-preliminary cooling to a temperature slightly above the temperature atwhich the wax begins to precipitate can be conveniently obtained in theheat exchanger 8. A continuous stream of this dewaxing solution is mixedwith a continuous stream of cold refrigerant, such as chilled propane,in the mixer I2 at a temperature of 0 F. to -44 F. or lower. This mixingof the continuous streams suddenly chills the dewaxing solution 20 ormore. 'I'he substantially instantaneous chilling may be serve enough toprecipitate most of the wax. The propane is then evaporated on theelongated passageway formed by the chilling coil 2| or in the chamber 23to chill the solution to the desired dewaxing temperature. The quantityof propane employed may be just sufficient to produce the predetermineddewaxing temperature, and in this event, approximately all of thepropane will be evaporated from the dewaxing solution. The precipitationof wax will then be determined by the nature of the normally liquiddewaxing solvent, and the function of this solvent as a wax-precipitantwill not be impaired by the presence of a substantial quantity of therefrigerant. We thus obtain the advantages of propane, or other normallygaseous material, as a refrigerant, without the disadvantages ofchilling to extremely low temperatures.

As a very specific example we will refer to the dewaxing of aMid-Continent lubricating oil distillate having an A. P. I. gravity of23.8, a Saybolt Universal viscosity of 74 at 210 F. and a pour point of110 F., which we dewaxed at 0 F. and obtained a lubricating oil having apour point of 5 F. As a dewaxing solvent we employed a blend of percentisopropyl acetate and 20 percent amyl acetate. One volume of thewax-containing distillate may be mixed with 3 volumes of said dewaxingsolvent at a temperature of 120 F. at the mixer 5, the resultantsolution being cooled to F. in the heat exchanger 8. A continuous streamof this solution may be mixed with one and one-half volumes of coldpropane, at a temperature of 40 F. or lower, in the mixer l2. .In oneform of the invention, the wax-containing solution is thus suddenlychilled to about 40 F. to 60 F., and the resultant mixed stream entersthe elongated chilling coil 2| under a pressure of about 40 pounds persquare inch. The pressure is gradually reduced as the mixed streamprogresses through the elongated passageway formed by said coil 2|, andthe mixture is discharged from the passageway to the chamber 23 underatmospheric pressure or lower. In the example given, the mixture waschilled to 0 F. and dewaxed to produce a lubricating oil having a pourpoint of 5 F.

In another example, a blended lubricating oil stock consisting ofresiduum 40 percent, heavy distillate 30 percent and medium distillate30 percent, having a Saybolt Universal viscosity of at 210 F. and a pourpoint ,of 105 F., was dewaxed at 10 F. above 0 F. to obtain a. brightstock'having a pour point 5 F. lower than the dewaxing temperature. i

The sudden chilling at a rate in excess of 20 F. per minute (1200 F.vper hour), for example, about 350 F. per minute, does not result in anydiiculty during the step of removing the wax from the solution. Actualtests have shown that the suddenly chilled solution can be Very rapidlyltered, so as to obtain the important advantage of very rapid chilling,as well as rapid and efiicient filtration.

This extremely sudden chilling may be practically instantaneous. Forexample, a drop of approximately 40 F. can be obtained in about 5 to l0seconds, which would be a rate of 240 F. to Ll80 F. per minute, theequivalent of about 14,400P F. to about 28,800D F. per hour. The-average chilling rate for the extremely sudden chilling combined `withgradual chilling in the coil 2| may be in excess of 1200 F. per hour.

The cold stream of liquefied normally gaseous refrigerant, which entersthe stream of solution at the mixer I2, could be at a temperature so lowthat further chilling is unnecessary. However, it is most convenient toevaporate the refrigerant as the mixed stream advances through anelongated passageway, thereby reducing the temperatur-e to the desireddegree and also removing the refrigerant from the mixture to be dewaxed.Or, instead of using the elongated passageway in the chiller 2|, andeven without previous chilling of the normally gaseous liqueedrefrigerant, the mixture could be transmitted under pressure through theby-pass 39, and thence into the chamber 23, where the pressure may bereleased to evaporate the refrigerant from the mixture to be dewaxed. Inthis event, the chamber 2S could serve vas an ordinary batch Chiller, orevaporator. In either case, the normally gaseous refrigerant could beintroduced into and removed from the normally liquid dewaxing solution,so as to permit separation of the wax in a simple apparatus, under aboutatmospheric pressure. By eliminating the normally gaseous refrigerantafter it has chilled the normally liquid solution, one can then dispensewith high pressure in the subsequent operatic-ns, and also overcome anyundesirable effect that the refrigerant may have upon the pour point orother'p-roperties of the dewaxed product.

It will now be understood that we have disclosed a process wherein anormally liquid solvent and a normally gaseous refriger-ant may beemployed to obtain the combined advantages of these two different typesof materials, without incurring the outstanding disadvantages heretoforeinvolved in using either of said materials. Furthermore, we havespecifically shown how to accomplish this result in a simple continuoussystem, where streams of the several materials are constantly flowingthrough the system, while maintaining a constant condition at any givenpoint in the system, and Without requiring the use of expensive andtroublesome batch chambers, or the like, where there is a frequentchange in either pressure, temperature, or volume of material. However,it is to be understood that the invention is not limited to speciiiccombinations herein disclosed, except as specified in the claims whichare intended to cover equivalents and modications of the severalfeatures herein specifically described.

We claim:

1. In the art of separating wax from lubricating oil stocks, the methodwhich comprises mixing the wax-containing oil with a normally liquiddewaxing solvent at a temperature high enough to dissolve the Wax andoil in said dewaxing solvent, continuously introducing a cold stream ofliquefied normally gaseous refrigerant into a stream of said solution tosuddenly chill the solution and quickly precipitate wax therein,transmitting the mixture in the form of a continuous stream through anelongated passageway and at the same time gradually evaporatingapproximately -all of the refrigerant in the flowing mixture togradually continue the chilling and precipitation of Wax, separating therefrigerant from the chilled mixture, and thereafter removing the waxfrom the chilled solution of oil and normally liquid dewaxing solvent.

2. In the art of separating wax from lubricating oil stocks, the methodwhich comprises mixing the wax-containing oil with a normally liquiddewaxing solvent at a temperature high enough to dissolve the wax andoil in said dewaxing solvent, the ratio of said oil and normally liquiddewaxing solvent being suicient for precipitation of the wax to beremoved in the process, cooling a continuous stream of the solution ofvwax-containing oil and normally liquid dewaxing solvent, continuouslyintroducing a cold stream of liqueed propane into said stream ofsolution to suddenly chill the solution and quickly precipitate waxtherein, transmitting the mixture in the form of a continuous streamthrough an elongated passageway and at the same time graduallyevaporating approximately all of the propane in the owing mixture togradually continue the chilling and precipitation of wax, separating thepropane from the chilled mixture, and thereafter removing the wax fromthe chilled solution of oil and normally liquid dewaxing solvent.

DWIGHT B. MAPES. EDDIE M. DONS.

